Final answer:
The order of cell junctions observed in the junctional complex from the apical surface to the basal surface of an epithelial cell is tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.
Step-by-step explanation:
The order of cell junctions observed in the junctional complex from the apical surface to the basal surface of an epithelial cell is as follows:
- Tight junctions: These junctions separate the cells into apical and basal compartments and block the movement of substances through the extracellular space between the cells.
- Adherens junctions: These junctions use either cadherins or integrins to link with adjacent cells, and they are characterized by the presence of the contractile protein actin.
- Desmosomes: These junctions occur in patches on the membranes of cells and hold cells together through the adhesion molecule cadherin.
- Hemidesmosomes: These junctions link cells to the extracellular matrix, such as the basal lamina, using adhesion proteins called integrins.
- Gap junctions: These junctions form intercellular passageways between cells, allowing for direct communication and the exchange of ions and small molecules.